Multipathing is a
technique that lets you use more than one physical path that transfers data
between the host and an external storage device.

In a simple multipathing local
storage topology, you can use one
ESXi host with
two HBAs. The
ESXi host
connects to a dual-port local storage system through two cables. This
configuration ensures fault tolerance if one of the connection elements between
the
ESXi host and
the local storage system fails.

To support path switching with
FC SAN, the
ESXi host
typically has two HBAs available from which the storage array can be reached
through one or more switches. Alternatively, the setup can include one HBA and
two storage processors so that the HBA can use a different path to reach the
disk array.

In FC Multipathing, multiple
paths connect each host with the storage device. For example, if HBA1 or the
link between HBA1 and the switch fails, HBA2 takes over and provides the
connection between the server and the switch. The process of one HBA taking
over for another is called HBA failover.

FC
Multipathing

If SP1 or the link between SP1
and the switch breaks, SP2 takes over and provides the connection between the
switch and the storage device. This process is called SP failover.
ESXi
multipathing supports HBA and SP failover.

After you have set up your
hardware to support multipathing, you can use the
vSphere Web
Client or vCLI commands to list and manage paths. You can perform
the following tasks.